The molecular heterogeneity of human collagens has been well established, and these various molecular species are now known to comprise a family of closely related proteins. In 1976, we described the identification and partial characterization of 2 new, structurally distinct collagen chains which we provisionally termed alpha A and alpha B. Suggestive data indicating that these chains might be components of a single new collagen molecular species of chain compositional formula alpha A (alpha B) 2 was also presented. The existence of these collagen chains has been subsequently repeatedly confirmed, and studies of the tissue distribution of these materials has indicated both that alpha A and alpha B are widely distributed, and are localized in intimate association with cell membranes and at least some basement membranes. The premise of this renewal application, as was the case for the original proposal, is that detailed structural information regarding alpha A and alpha B at the level of cyanogen bromide peptides, whole chains and native molecules will be critical for structure-function correlations, discernment of homology between collagens, and, as is suggested in this proposal, possible structural definition of a new class of "cell-associated" collagens. Companion studies aimed at definition of tissue distribution and micro-localization of this new collagen should yield further information regarding function and together, the chemical and immunolocalization studies will set the stage for extension of these studies to various human disorders such as diabetes mellitus, Marfan syndrome and others.